This invention relates to a mobile lifting device for the disabled and, in particular, to a lifting device which provides a number of safety features in a coordinated fashion such that the safety features do not encumber the normal operation of the device.
Under the Americans with Disabilities Act of 1990 ("ADA"), the government of the United States of America required that public buildings be accessible to the disabled. For persons requiring a wheelchair for mobility, abrupt changes in floor elevation have to be modified to enable access by wheelchair. For new construction, a ramp is typically provided and the pitch or grade on the ramp can be no greater than one inch of rise per foot of horizontal travel and a horizontal landing five feet in length must be provided for every thirty inches of vertical travel. For older buildings or where space is limited, the requirement for a ramp can cause a problem.
The ADA also permits a vertical lifting device instead of a fixed ramp. Typically, the lifting device is permanently mounted and includes a short ramp for entering a small car which is raised and lowered by a suitable jack mechanism. Under ADA, such lifting devices must have side walls no less than forty-two inches high and include a grab bar on one side wall. Travel surfaces must be non-skid and a safety skirt must enclose the jack mechanism. A "toe guard", for detecting obstructions under the car when the car is being lowered, must also be provided.
Known fixed lifting devices include solid side walls and often omit a gate on one end of the lifting device. Such lifting devices can be uncomfortable to ride if one is claustrophobic or a young child and the open end is unsafe. In many or most cases, the obstruction is less than about forty-two inches high, e.g. the elevation of the first floor above ground level in many buildings or the height of a stage. As used herein, "stage" refers to an elevated floor, whether or not the elevated floor is actually a stage in a theater or in an auditorium.
Mobile lifting devices for the disabled are known in the prior art, e.g. as described in U.S. Pat. No. 5,105,915 (Gary) which describes a lifting device having a car including fixed sides and short, one-piece ramps at each end. The car is raised and lowered by a pantograph jack including a hydraulic pump driven by an electric motor controlled by switches. The patent also describes several lifting devices of the prior art.
A problem with safety devices is that they are often an impediment rather than an aid. Safety interlocks which must be operated by the able-bodied may be a bother but, for the disabled, the interlocks can be an impediment to using what may otherwise be a helpful device. The car in a mobile lifting device is inevitably placed a slight distance from a stage, requiring a docking plate to bridge the gap between the car and the stage. If there is a gate at each end of the car, operating the docking plate and the gate can be a task which a disabled person may not be particularly adept at performing.
ASME (American Society of Mechanical Engineers) standard A17.1 requires lifting devices, except elevators, to have control switches which are effective only when actuated; i.e. momentary contact switches must be used for motion control and raising or lowering the car in a lifting device may occur only while a switch is actuated. The electrical controls of the lifting device must also be manipulated by the disabled person, further complicating the operation of the lifting device.
Having an attendant accompany a disabled person does not necessarily solve the problem of needing manual dexterity to operate a lifting device of the prior art. The attention of the attendant is supposed to be directed to the disabled person, not to operating the lifting device. An attendant could be distracted at a moment of need.
In view of the foregoing, it is therefore an object of the invention to provide a lifting device for the disabled in which the device includes several safety features which are transparent to an operator.
Another object of the invention is to provide a lifting device in which the car can be safely raised and lowered by a passenger or an attendant.
A further object of the invention is to provide a lifting device which can accurately position the car vertically without elaborate calibration.
Another object of the invention is to provide an electrically controlled lifting device which can be lowered despite a power failure.
A further object of the invention is to provide a lifting device for the disabled in which the vertical motion of the car can be stopped at any point by the passenger or an attendant.
Another object of the invention is to provide a lifting device for the disabled in which the car is operated by an attendant to the exclusion of the passenger.
A further object of the invention is to provide a lifting device for the disabled in which the car is operated by an attendant to the exclusion of the passenger, except for emergency stops.
Another object of the invention is to provide a control system for a lifting device in which motion in one direction continues as long as a switch is actuated irrespective of the operation of any other, non-emergency control switch.
A further object of the invention is to provide a control system for a lifting device in which the device is prevented from operating if a plurality of conditions are not met.
Another object of the invention is to provide a control system for a lifting device which gives a visual indication that the car is elevated to the proper height and that a latch is opened, permitting egress from the car.